Keying control system for oscillators



Oct. 19, 1948. STVQRM ET AL 2,451,887

KEYING CONTROL SYSTEM FOR OSQILLATORS Filed Nov. 20, 1946 2 Sheets-Sheet 1 Inventors: Herbert F. Storm, EPneSC W. Hutton,

Their" Attorney.

Oct. 19,1948.

Filed Nov. 20, 1946 H. F. STORM ET AL 2,451,887

KEYING CONTROL SYSTEM FOR OSCILLATORS 2 Sheets-Sheet 2 Fig.4. M 5? g1 A gml g i xj i g m if 1:

ES Fig.5;

Irflvntors:

Hernbert FT Storm,

Erne st W. Hutton,

Their" Attorney.

Patented Oct. 19, 1948 ;KEYING.-CONTROL SYSTEM FOR vOSCILLATORS Herbert Storm and Ernest W; HuttomSehenectady, N. Y;, assignors to'General Elec'tric'Company, a corporation of New York ApplicationNovember 20, 1946,..SeriaI No.7 1I,164

2-0laims. (Cl; 250-36) This invention relates to control systems, and

more particularly to systems for controlling keying operations of high power electric valve type "oscillators, and it has for an object the provision of a simple, reliable and improved control system f of this character.

. Another object of the invention is the provision of a keying control system which effects substantial economies in the electrical power consurned. in the keying operation. Still another object is to provide increased. reliability and to effect economies in maintenance by minimizing the burning out of parts. In electric valve oscillators, the grid bias voltage is usually obtained ventionpandFigs. 2, 3, =4 and 5 are characteristic curves which facilitate an understanding of its operation.

Referring now-to the drawingy'anoscillator l 5 is supplied from-a suitablesource of "voltagewhich is-representedby the terminal 2' and the ground connection 3. "Although this oscillator may be of any suitable-type, it is'illustrated as a conventional class C Cclpitts-oscillator.

0 The tank-circuit of the oscillatorcomprises the inductance tandthe capacitors Sand 6. The coupling between the tank' circuit and' the anode and'grid circuits comprise-the capacitors -'I' and 8.

A negative bias voltage forthe grid'Sa of the oscillator valve 9- isobtained from the'voltage dropacrossa grid biasresisto'r ID in which a 'direct current is "obtained by means of-grid rectification. lamp bank comprising a number of incandescent Thegridbiasingresistoris'preferably alamp bank lamps connected in series. In high power oscilcontaining a plurality orincandescent-lamps lfla, lators, a number in excess of such lamps fre- 20 iObg-Wilcjifld, etcfl' A'lthough the grid bias requently is required for the grid bias resistor. sistorisillustrated'ascomprising only four lamps, Accordingly a more specific object of the inven it is un'clerstood"thatinpractice a-much larger tion is the provision of a relatively low power um r f a ps s' p y example, in control system for supplying to the bias resistor ajtypi a-l'hi h'p w d s i lat 'the' r d as r a negative variable voltage which is just sufficient sistorcomprises-23*suchlamps. to terminate the oscillations and to maintain the During normal op e'i' the osciloscillator turned on for a period vwhichnvaries "lating "period; current-flows through the 'bias refrom a fraction of a second to several minutes or SuCh dir t n. t a n a ias V0113- longer periods of time. --age -vvith-'respect to ground.- is produced at the In carrying the invention intoefiectinone terminalll. ""-This condition isy=represented in form thereof, a relatively high power electric valve Fig. 2 in Y which ordinates rep ese t "Vo e a d .type oscillator is provided with a. grid. bias resistor c a rep esent't me- Grou'nd'voltage is repin'which a direct current is obtained by means of s y thehorizontal'lin'e UiJandthenegagrid rectification. The. grid bias voltage is ob- 't'ivegrid bi s volt e ier pr n y t h ritained from the voltage dropacross this resistor. -Zontalline l2.

For the purpose of controlling or keying the-oscil- During t DBIi d' Oscillation a p n' the vlator, i. e. turning the high frequency power on "*tank-circuithigh eq e yvo ta e s up ed or on at will for periods varying from a fraction to=the gridc 'cuit e Coupling p rs of a second to a few minutes, means are provided 1 and 8." 'The"totargrid-v t is thus the Sum for supplying to the bias resistor a negative-pulse 40' of 'the bias voltag Ec' 'afidfih hi r qu y Voltage of sufficient Inggnjtude t m t t voltage which is'obtained from the" tank circuit oscillations. This'pulse voltage is decreased in sr pr t h y t us idal curve l3. magnitude at a rate substantially equal to the fi t "Cll ei 'WhiCh the .rate of decay of the high frequency oscillations. "grid'voltage iS" fi ;cu t fiOWs in'the anode At the termination of the oscillations a hold-off cilfluit 0f Oscillatorwalve 9." hiS Current is voltage is supplied to the bias resistor of which 'l'lecessary'to'sllstainthe iI at II from the voltage across a resistor in the grid circuit in which direct current is obtained by grid rectification. This grid bias resistor may be a the. magnitude is substantially less. than the value required to terminate the oscillations but is suiiicient to maintain the oscillator inactive once the oscillations have been terminated.

For a better and more complete understanding of the invention, reference should now be had to the following specification and to theaccom- For the purpose of" 'stoppingthe oscillation,

means are provided for supplying a negative pulse voltage to the grid circuit to increase'theoriginal .equal to the crestvalue of the grid voltage Eg max. of the grid voltage Ego For. reliable operation,

panying drawings of which Fig. 1 is a simple, :..schematic diagram of an embodiment of, the inthelbias. voltage should bev made more negative ,by an additional marginal amountEm. Thus; the

tinuous basis without burning out the lamps; 2,

in energizing the grid bias resistor from an external source having a voltage Es, a large amount of power is consumed. The prevention of oscillations can be accomplished by a much smaller bias voltage than that which is required to initiate the termination of the oscillations. Consequently, maintaining the negative bias voltage throughout the stopping period at the value Es would result ina very considerable waste of power.

In order not to waste power, a negative pulse voltage is supplied to the grid circuit which is of suificient magnitude to initiate the termination of the oscillations. This pulse voltage is followed by the application of a moderate bias volt age which at any instant is just large enough to prevent a resumption of oscillations.

In Fig. 4 the grid voltage Eg of the oscillator is first shown during a normal oscillating condition. It is represented by the sinusoidal portion I4 of the curve. At the time To the stopping pulse Es is applied between the terminal II and ground. This pulse forces the gridvoltage negative to such an extent that the grid voltage re- 1;-

mains negative and the flow of anode current in the oscillator valve is prevented. As a result the oscillations in the tank circuit 4, 5, B will decay and the high frequency voltage which is supplied from the tank circuit to the grid circuit will also decay as represented in Fig. 4 by the sinusoidal curve I la. of diminishing amplitude. in a conventional oscillator a much greater number of cycles than illustrated .in Fig. 4 will be required before the residual oscillations may be considered to be negligible. It may be assumed that this condition is attained at the time T1. Then the stopping pulse Es may be terminated and a moderate holding bias Em will suffice to prevent oscillations from starting.

If a rectangular-shaped stopping pulse voltage, such as illustrated in Fig. 4, is applied, the marginal safety voltages Emi, Emz, E1113 for the successive cycles become larger than necessary, since the high frequency voltage supplied from the tank circuit to the grid circuit begins to decay at the instant of application of the stopping pulse.

The marginal safety values of voltage are prevented from exceeding the necessary value for successive cycles by applying a pulse voltage of declining amplitude, with the result that the component parts for generating such pulse become smaller and less expensive because the pulse or declining amplitude takes less energy than the rectangular pulse. energy dissipated in the lamp bank grid bias resistor is reduced to a value that will not burn out the lamps.

For the purpose of supplying to the grid circuit a negative voltage of diminishing magnitude, a circuit which includes the rectifier valve I5 and a capacitor I6 is provided. This rectifier valve is supplied from a suitable source of alternating voltage which is represented by the supply lines I! to which the valve is connected Furthermore, the

4. through the primary winding I8a and secondary winding IBb of a transformer I8. The rectifier valve I5 and the transformer I8 constitute a trickle charger which charges the capacitor I6 through a resistor I9 to the voltage Es which is required to initiate the termination of oscillations. One terminal 'of the capacitor I6 is connected by means of the conductor to the terminal I I in the grid circuit of the oscillator valve. A thyratron valve 2| is connected between the other terminal of the capacitor I6 and ground. The high voltage to which the capacitor I5 is charged is impressed across the grid bias resistor In by the firing of the thyratron valve 2|.

A direct voltage for controlling the thyratron 2| is obtained from the source I! by means of a full wave rectifier valve 22 to which it is connected through the transformer 23. The rectified voltage is filtered by means of capacitors 24 and 25 and inductance 2G and is supplied to the terminals of a voltage divider comprising resistors 21, 28, 29 and 30. As shown, the cathode 2Ib of the thyratron is connected to the grounded common point of the resistors 29 and 30 of the voltage divider, and the grid 2 lo is connected to the point between the resistors 21 and 28 of which the voltage is negative with respect to the point to which the cathode is connected. Thus, the thyratron 2I is maintained at cut-off.

For the purpose of providing a hold-off voltage after the stopping pulse voltage has decayed to the hold-01f value, a polyphase rectifier 3| is provided. This rectifier is illustrated as comprising a plurality of thyratron valves 32, 33 and 34 and a transformer 35 having a delta-connected primary winding 35a and a Y-connected secondary winding 35?).

The primary winding 35a. of the transformer is supplied from a suitable source of polyphase voltage which is represented by the three supply lines 36 to which it is connected by means of an auto transformer 31. The positive output terminal 3Ia of the rectifier is connected to ground, and the negative terminal 3!!) is connected to the terminal I I of the grid bias resistor.

The rectifier 3I is arranged for 3-phase operation in order to prevent the hold-oif voltage from ever decreasing to zero. The polyphase rectifier having the least number of phases whose voltage never reaches zero without a filter is a 3-phase rectifier.

While the oscillator is oscillating this rectifier is ready to fire. The grids of the three valves 32, 33 and 3.4 are efiectively grounded through the resistor 38. However, while the oscillator is oscillating the rectifier valves will not fire because the negative voltage from the grid bias resistor which is applied between the output terminals 3Ia. and 3Ib of the rectifier exceeds the anode voltages supplied by the transformer secondary winding 351). In other words, the anode voltage of the valves 32, 33 and 34 will be negative during oscillation.

For the purpose of initiating the termination of oscillations at will, a switching device 39 and an electromagnetic contactor 40 controlled thereby are provided. The switching device 39 is illustrated as amanually operated push button type switch having normally open contacts 39a.

With the foregoing understanding of the elements and their organization, the operation of the system will be readily understood from the following detailed description.

voltage is represented by the sinusoidal curve 4! in Fig. 5. Since the push button switch 89 is open and the con-'tactor 4G is in the deenergized condition, the grid 210 of the thyratron i?! is connected to a point on the voltage divider 2'1, 28, 29 which is so negative with respect to the voltage of the cathode ilb that the thyratron is non-conducting. As a result, the capacitor 56 is charged to maximum voltage by means of voltage supplied from the transformer i8 and rectifier valve l5.

It is assumed that it is desired to terminate the oscillations of the oscillator at a time To. This is accomplished by closing the contacts of the push button switch 39 thereby to complete an energizing circuit of the operating coil of the contactor 40. In response to energization, the contactor 40 closes its normally open contacts 40a and Mb and opens its normally closed contacts 48c and 40d. In closing, contacts 49a momentarily connect the grid 21c of thyratron 2| to ground through the capacitor 42. As a result, the thyratron 2! is rendered conducting and capacitor 55 'is discharged through the thyratron thereby applying a negative pulse voltage between ground and the terminal ll of the grid bias resistor ID. This negative pulse voltage is represented in Fig. 5 by the voltage Es at time To.

The discharge of the capacitor is, which reduces the anode voltage of thyratron 2!, to gether with the buildup of a negative voltage on the grid Me, as a result of the charging of capacitor 42, will prevent continued firing of the thyratron and permit only one discharge of the capacitor l6 for each closure of the contacts 40a. The decay of the stopping pulse volt age which is supplied by the capacitor E6 to the grid circuit of the oscillating valve is represented in Fig. 5 by the logarithmic curve 43.

At the time T1, the grid voltage has decayed to the value Ech which is the value required. to prevent oscillations from being initiated. At this time the voltage impressed on the output terminals of the polyphase rectifier 3! from grid bias resistor becomes less than the voltage of the rectifier and consequently the rectifier impresses a negative hold-oil voltage between ground and terminal II. This hold-oiT voltage is sufficient to prevent further oscillation.

'I'o res-tore the condition of oscillation, the valves 32, 33 and 34 are prevented from firing thereby removing the negative hold-off voltage which is supplied to the grid bias resistor 10. This is accomplished by releasing the push button switch 39 to interrupt the energizing circuit for the operating coil of the contactor 40. In response to deenergization the contactor 40 opens its normally open contacts 40a and 40b and closes its normally closed contacts 490 and 4801. During the time when the contacts 4% were closed, the capacitor 114 became charged from the voltage across the resistor 29 of the voltage divider. The polarity of the voltage of the capacitor 44 is plus at the ground terminal and negative at the grid terminal. Consequently,

when the contacts 40d close, negative voltage is impressed on the grids of the valves 32, 33 and 34, with the result that these valves cease conducting. As soon as the hold-off voltage disappears, oscillation is resumed in a normal manner. I

Although in accordance with the provisions of the patent statutes this invention is described. as embodied in concrete form and the principle thereof has been explained together with the best mode in which it is now contemplated applying that principle, it will be understood that the elements shown and described are merely illustrative and that the invention is not limited thereto since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims.

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination an electric valve oscillator comprising an electric valve having a cathode and a control grid and a bias resistor connected between said grid and cathode, means for termi nating the oscillations of said oscillator comprising a circuit in parallel with said bias resistor including a capacitor and a second electric valve, means for charging said capacitor and means for firing said second valve to discharge said capacitor to supply to said grid a negative pulse voltage having a rate of decay substantially equal to the rate of decay of said oscillations, and means for supplying to said grid a negative holdoif voltage having a substantially smaller magnitude than said pulse voltage.

2. In combination an electric valve oscillator comprising an electric valve having a cathode and a control grid and a bias resistor connected between said grid and cathode, means for termi-- mating the oscillations of said oscillator compris ing a circuit in parallel with said bias resistor including a capacitor and a second electric valve, means for charging said capacitor and means for firing said second valve to discharge said capacitor to supply to said grid a negative pulse voltage having a rate of decay substantially equal to the rate of decay of said oscillations, means for supplying to said grid a negative hold-on? voltage having a substantially smaller magnitude than said pulse voltage comprising a polyphase rectifier having its direct current terminals connected to said bias resistor, and means for supplying a polyphase alternating voltage to said rectifier smaller in magnitude than the portion of the bias voltage across said terminals whereby said rectifier is maintained inactive during oscillation.

HERBERT F. STORM.

ERNEST W. HUTTON.

REFERENCES CITED UNITED STATES PATENTS Name Date I-Iausz Aug. 19, 1947 Number 

